All servers use IP tables to decide what can access the server and how. If you are blocked from a certain service you can normally gain access by logging in as root and running a command to clear the IP tables. This code is: 

To flush a Single Chain

To flush a specific chain, which will delete all of the rules in the chain, you may use the -F, or the equivalent --flush, option, and the name of the chain to flush.

For example, to delete all of the rules in the INPUT chain, run this command:

sudo iptables -F INPUT

To flush All Chains

To flush all chains, which will delete all of the firewall rules, you may use the -F, or the equivalent --flush, option by itself:

sudo iptables -F

If you already added a Firewall program like CSF, you would want to use this CSF command to flush the block which is:

csf -f